1. Field of Invention
The invention relates to a magnetic electronic device and a manufacturing method thereof and, in particular, to a magnetic electronic device and a manufacturing method thereof wherein the magnetic property of the free layer is adjusted.
2. Related Art
The concept of magnetic random access memory (MRAM) was brought up by Andreas Neyc with his colleagues of the Paul Drude institute in Germany. In MRAM, ferromagnetic metal is used and the data bit is stored by different relative magnetization alignment of the recording layer (free layer) and the reference layer (pinned layer), where parallel and anti-parallel magnetization alignment can result in low resistance level and high resistance level due to magnetoresistance (MR) effect, respectively. The data bit of a MRAM cell can be written by applying external magnetic field or current to reverse the magnetization direction of the recording layer. Different from static random access memory (SRAM) or dynamic random access memory (DRAM), MRAM is one kind of non-volatile memory since the stored data can be maintained until next external magnetic field or current is applied to reverse the magnetization direction. Both SRAM and DRAM are volatile since they need external periodic current supply all the time to retain the stored data, and therefore lots of unwanted heat would be generated and the power consumption is relatively large. Moreover, MRAM cell can be reset by ultra-short pulse field or current within only a few nanoseconds which is faster than the response speed of SRAM and DRAM. In short, MRAM possesses lots of advantages over SRAM and DRAM and is considered to be one of the most promising candidates for the next generation random access memory application.
In early days, MRAM cell is made by the effect of anisotropic magnetoresistance (AMR) to create different resistance levels, but the generated signal is too small to meet the practical requirements. MRAM didn't get vigorous development until the findings of giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) effects which can much enhance the signal level. Currently, the most commonly used materials of the magnetic tunneling junction (MTJ) is the structure of two CoFeB layers (i.e. ferromagnetic layer, both free layer and pinned layer) separated by one MgO layer (i.e. insulating layer) that are made by ultra-high vacuum sputtering method. After the as-grown amorphous CoFeB experiences an annealing treatment, a good texturing (001) can be generated at the interface of CoFeB and MgO, and such texturing results in considerable magnetoresistance. This related process of the structure is easier than epitaxial process and is more suitable for mass production, therefore becoming the mainstream in MRAM industry. MRAMs are usually made by magnetic materials with in-plane magnetic anisotropy nowadays. However, materials with perpendicular magnetic anisotropy are more usable than the in-plane devices since having higher recording density and theoretically smaller switching current density for spin-transfer torque, and thus becomes a focal topic for the researchers.
After H. Ohno's team from Tohoku University in Japan announced the magnetic tunneling junction of CoFeB/MgO with perpendicular magnetic anisotropy, such materials system has become the most promising candidate for MARM. In comparison with other competitors with perpendicular anisotropy such as cobalt-based multilayers or L10-ordered alloys, its better texturing (001) at the junction ensures extremely high magnetoresistance. However, usually the thickness of CoFeB cannot exceed 1.5 nm in order to maintain its perpendicular anisotropy. In all related literatures of CoFeB with perpendicular anisotropy, the unit-volume saturation magnetization of CoFeB has only reached 1000 emu/c.c., and the magnetic anisotropy energy thereof is still insufficient. The thermal stability factor, which is defined as the ratio of the magnetic energy to the thermal energy, is around 40 at most in all presenting works for CoFeB with perpendicular magnetic anisotropy, which is still below the required value of a stable recording media for 10-year-storage (>60) and therefore the applicability thereof is limited.
In practical MRAM manufacturing process, manufacturing a MTJ (magnetic tunnel junction) itself is a big challenge, but other problems will also be encountered in the integration of the front-end and back-end processes. The most important problem in those processes is the thermal budget of MTJs. Typical BEOL (back-end-of-line) process requires a high temperature forming gas annealing above 400° C., and usually the component would lose its perpendicular anisotropy after such high temperature treatment.
Therefore, it is an important subject to provide a magnetic electronic device and a manufacturing method thereof wherein the saturation magnetization and perpendicular anisotropy of the bilayer structure of CoFeB/oxide can be increased and the thermal stability and thermal endurance of the CoFeB layer (magnetic layer) can be enhanced a lot.